Dennis was a forward with Manchester United, where he scored 179 goals in 294 matches and played a big part in the winning of League Championships in1956 and 1957. He moved to Stoke City in 1962; the team won two Second Division Championship medals and one League Cup runners’ up medal. He coached the Washington Diplomats of the NASL for several years, and then moved to the New England Tea Men. The team relocated to Jacksonville, where Dennis became head coach at Jacksonville University. He then joined the Richmond Kickers, who in 1995 won the USISL Premier League title and the US Open Cup championship. Dennis finished his coaching career with the A-League Jacksonville Cyclones.